Piezoelectric phenomenon basically is an energy conversion process between mechanical energy and electric energy. As electric charges and strain have a cause and effect relationship, a substance that can generate piezoelectricity and has a crystal structure can produce an electron dipole moment when subject to an external force. Hence energy conversion between mechanical energy and electric energy occurs. This is the fundamental principle of piezoelectricity.
Generation of the electron dipole moment is caused by a special arrangement of positive ions and negative ions in a crystal. Different crystal lattice systems in materials result in generation of different electron dipole moments. The basic condition is that a crystal lattice has an asymmetric center. If a symmetrical center exists in a crystal lattice, the positive ions and the negative ions are neutralized, then the electron dipole moment does not exist, and energy conversion between the mechanic energy and electric energy does not occur. The conversion of mechanic energy and electric energy generally has three types: 1. convert mechanic energy to electric energy; 2. convert electric energy to mechanic energy; 3. convert electric energy to mechanic energy then to electric energy to be output. Piezoelectric ceramic has piezoelectric characteristics that can perform conversion between mechanic energy and electric energy, thus is widely used, such as in pressure sensing elements, speed accelerators, micro-motors and the like. Moreover, piezoelectric membrane is desirable for electronic products that demand thin and light. It can be used on electronic elements in bio-sensors and communication, hence is quite popular in academic and industrial applications.
In 1973, Berlincourt discovered a “Unipoled PZT” piezoelectric structure. By changing the thickness relationship between the output/input area and a corresponding polarization area of a piezoelectric structure, the voltage boosting and reducing ratio of the piezoelectric structure can be altered during the polarization process. However, in the conventional practice, the distance of the input and output electrodes and the ground electrode remains constant to alter the polarization area of the input and output electrodes to change the voltage boosting and reducing ratio.
U.S. Pat. No. 3,764,848 discloses a piezoelectric structure for activating a gas charge lamp. It mainly adopts the principle mentioned above, namely by changing the polarization area ratio covered by the input and output electrodes to get different output voltage boosting and reducing ratios, thereby to actuate the gas discharge lamp.
By means of the aforesaid approach, in the condition of a higher voltage boosting ratio, the input and output voltage are on the same surface. The potential difference between the input electrode and output electrode is great either in the voltage boosting or reducing condition. Located on the same surface, the input and output electrodes also cannot be spaced at a desired interval. As a result, sparking phenomenon frequently occurs between the electrodes. This easily causes rising of temperature and results in the risk of fire breakout in the surrounding environment.